Complex glycans, which are ubiquitously distributed at the interface of intercellular surfaces, act as receptors for various microbial pathogens and play a key role in determining the pathogen's hostcellular and tissue tropism. Despite their importance in host-pathogen interaction, it has been challenging to bridge the biochemical and biophysical specificity of glycan-protein interactions with the biological functions modulated by these interactions. These challenges arise from the difficulties in characterizing the fine structural granularity of glycan receptors in their physiological context such as epithelial surface of different tissues. Therefore there is a need to bridge the structural characterization of glycans at the tissue, cellular and molecular levels. Decoding the diversity of the physiological glycan receptors at these levels would not only facilitate the identification of glycan receptor targets from the standpoint of understanding pathogenesis but would also facilitate development of therapeutic strategies to counter pathogen infection. We have begun to address the above issues by developing a multifaceted framework to decode the structure-function relationship of glycan-protein interactions. Using a combination of lectin staining of tissues and mass spectrometry based structural profiling of glycans isolated from representative cell types we have taken a step towards bridging the characterization of glycans at the tissue and cellular level. Plant lectins have traditionally been used to investigate distribution of glycan structural motifs (recognized by the lectins) in the physiological context of cell and tissue surfaces. However, the diversity of glycan receptors based on lectin staining have been characterized in a abstract fashion or at best in terms of terminal glycan linkages such as a2-3 or a2-6 linked sialic acids. The abundant structural and biochemical information on glycan-binding properties of plant lectins offers tremendous potential to develop new strategies for using these lectins to probe into finer structural details of physiological glycans going beyond terminal linkages. Based on this information, lectins can be engineered to target interactions between pathogens and their host glycan receptors. Building on our previous efforts in this proposal we seek to develop strategies that utilize plant lectins in new ways to obtain more detailed structural characterization of physiological glycan receptors as well as develop these lectins to target pathogen-host glycan receptor interactions. PUBLIC HEALTH RELEVANCE: Complex glycans decorate biological surfaces specifically the interface of intercellular surfaces where they play a critical role in mediating cell - cell interactions such as host cell - pathogen interactions. There are challenges in bridging the physiological glycan receptor binding of pathogens with the biology of their pathogenesis and host adaptation. These challenges arise from the limitations in characterizing the fine structural diversity of glycan receptors in the appropriate physiological context such as specific cell and tissue surfaces. In this proposal we seek to address this issue by exploiting the untapped potential of plant lectins both to obtain a detailed mapping of the nuances in the structural features of the glycan receptors in physiological surfaces such as human upper respiratory epithelia and to develop these lectins as tools to competitively target these receptors.